Electrical motors are used in a variety of applications. These applications include refrigeration units, pumping systems, and the like. Typically, the input power to a power supply for operating an electrical motor or other electrical equipment can vary depending upon the environment in which the power supply will be used. Electronic controls are used to operate the electrical motors in a manner that attempts to optimize the efficiency of the motor, vary the output speed to reduce load power, and maximize the power output of the motor. In some applications, reducing the noise audible to humans is added to these goals.
In previously known electrical motor controls, quiet operation of multiple speed and variable speed motors is obtained by operating the motors at frequencies above the audible range to attenuate the noise produced by the motors to an acceptable level. For example, these higher frequencies that operate the motor are typically in a range of about 15.5 KHz to 20 KHz. These higher frequencies, however, produce higher losses in the motor and generate heat that must be removed. The inclusion of components to remove heat adds cost to the circuit. Being able to provide an electrical motor control circuit that improves motor efficiency and helps control noise without adding cost to the circuit would be useful.